misfire driving me crazy...

sinister5oh · Apr 20, 2016

hello, long time mustang fanatic, first time mustang owner.
i recently bought a 94 5.0...69k original miles (believe me).
the engine appears to be in great shape, considering its age. this is my problem:misfiring when hot. I'm sure that there's been plenty of threads about this problem alone but I feel obligated to post my own thread (I just joined this forum today). SO, when engine is at normal operating temp, it will misfire under load between 2-3k RPM usually. I have done some basic part replacements. Spark plugs checked out OK, must have been replaced recently. I regapped/cleaned. I replaced dizzy cap and rotor. I bought a new ignition coil. the connector for the coil wire seemed eaten away, as the coil wire was rusted to hell..which led me to replace the wires. I'm convinced this is an ignition problem, NOT a compression/fuel problem. the car runs GREAT for 20 minutes or so after cold start but after driving at normal operating temp, the misfiring begins. I'm pulling my hair out as I just want my first mustang ever to be running perfectly (hard to expect out of a 22 year old pony). HOWEVER, I'm headed to pick up a new ignition control module right now, as my dad stands my firmly that this could be the root of my problem. he is a mechanic and says he has seen problems similar to mine be directly related to the ignition module plenty of times. anyways I'm going to get the module now, if anyone wishes to chime in for any other possibilities of my misfire, it would be greatly appreciated. I will definitely keep you all posted on how the car runs after installing the new module.

sinister5oh · Apr 20, 2016

update: new ignition module, no improvement. I'm getting pretty frustrated now as I've spent a decent amount of money on parts I probably didn't need to begin with. suggestions/tips would be great..thanks.

96blak54 · Apr 20, 2016

Im lost ....and surprised no one else has posted. Ill ask a few of my fox body buds and report back

96blak54 · Apr 20, 2016

My buddies are saying the pickup in the distributor is bad. Typical ford failure. Possible the coil is cracked. Opens up when warm

g36 monkey · Apr 21, 2016

I was going to say try running a fuel cleaner just to see if it helps any. I have had fuel delivery issues that felt like ignition issues. could also be the fuel pump. Mine would not start to misfire until I drove for about an hour, and would cruise comfortably. The second I came down to a lower speed and needed to accelerate it would sputter and stumble.

ranger56528 · Apr 21, 2016

Make sure your MAF is clean and you have no vacuume leaks and maybe check tps voltage .98 .99 would be good.

sinister5oh · Apr 21, 2016

I ran fuel cleaner just two weeks ago, I could try another can of it. MAF is cleaned. Just replaced spark plugs tonight, problem still persists. 96blak54... should I replace just the pickup or the entire distributor? ranger56528... I've read up on TPS voltage for the 94-95 5.0's, and some people firmly stand behind there being no need for checking the voltage, as the different computer in the Sn95's automatically picks up the voltage it's given and works from there, unlike the fox's. they stated the "safe range" is from .8-1.2 volts. I was able to back probe and got a reading of 1.08, so I thought that was okay for me. I sometimes hear a whistle under the hood, which leads me to a believe it could be a vacuum leak..but I'm at a loss on how to check for a vacuum leak. I feel like the possible leak spots are endless. how can I check for leaks at home in my garage?

g36 monkey · Apr 21, 2016

I am so glad someone finally asked so directly!

Buy a cigar, a cheap cigar, a good cigar, whatever, a mechanic cigar.

Buy a match, or lighter, or torch, something to light the cigar.

Stand near your vehicle.

Pop the hood.

Remove the hose from the brake booster.

Light your cigar. Make sure you can get a good puff of smoke.

Exhale smoke into the brake booster hose.

Watch for leaks coming out of gaskets, hoses, etc.

It's normal for some to escape out of your throttle body.

This test has revealed several very tricky vacuum leaks for me. I am sure it will do the same for you!

sinister5oh · Apr 22, 2016

thank you g36 monkey, I'll be sure to try that. I'm thinking mostly that it's either the fuel pump, bad injector(s), or a vacuum leak...

evilcw311 · Apr 22, 2016

Mine did the same when my dizzy was dying. Replaced dizzy and problem went away.

Try the vacuum trick first then go to Oreiley and get a dizzy. Do not get one from autozone

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g36 monkey · Apr 22, 2016

You're welcome, I have posted it several times around here. Has definitely helped a number of people find their leaks. When you go to a shop and they check for vacuum leaks, they have what is essentially a $2,000 smoke machine to do the same test.

Since you don't need to do them that often, a cigar works just as well IMO.

sinister5oh · Apr 22, 2016

g36 monkey, I actually work at green ford in Greensboro, NC..I'm interning and going to school for automotive technology. so I can perform plenty of tests here at work, 'be just gt plenty more to learn lol. evilcw311, how much is a dizzy? should I really buy from an auto parts store or should I try online or even here through ford? I get 20% employee discounts on parts.

evilcw311 · Apr 22, 2016

Oreiley dizzy' have had the least issues of all replacement dizzy's

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95GT86SS · Apr 22, 2016

It's the rich porter remans that have had good reviews. If it starts missing at warm up it could be the dizzy. Does it have the CEL on?

95 GT BBK CAI TB MSD 6AL O/R H SLP LM1
Coming soon GT40 Heads Intake and e303 cam with Long tubes

sinister5oh · Apr 22, 2016

no CEL, that's what is bugging me. a tech here at work has plenty obd1 capable scanner, I've been meaning to pull codes and/or run a possible test. it starts up ok, sometimes takes a few seconds until it actually turns over, but when cold it doesn't idle high likes it's supposed to, it will drop down to normal idle after startup. when pulling out of driveway when still cold, it is a little difficult to get going and will hesitate. after 60 seconds, response feels okay. then, when at normal operating temp, the misfiring begins. anyone almost 100% sure I should go with dizzy replacement? if it was fuel pump, I would have poor acceleration all the time, instead of just when warm, am I correct?

sinister5oh · Apr 22, 2016

I also should have mentioned, it has an F303 cam, longtubes, no cats, JLT cold air intake...

evilcw311 · Apr 22, 2016

Has it bn tuned??? Mine has b303 with full custom exhaust no cats and it didn't run great till I had adder burn me a chip, but I had also removed all emissions. No egr no smog no nothing

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sinister5oh · Apr 22, 2016

I'm assuming it's been tuned...lol the cam was probably installed around 2000.... I think I may need to adjust my timing though, I will be doing that. but this misfire (according to the previous owner) was not present ever. there's only 69k original miles, it's been sitting (not for years on end, just not driven a lot). I just want to cure this cancer already!!

95GT86SS · Apr 22, 2016

I'd go the dizzy route first.

95 GT BBK CAI TB MSD 6AL O/R H SLP LM1
Coming soon GT40 Heads Intake and e303 cam with Long tubes

sinister5oh · Apr 22, 2016

If it's not the distributor, and I can't find any vacuum leaks, what should my next plan of action be?? is there any way to inspect fuel injectors..? can injectors cause misfire only under normal operating temp?